Issue 72

M. A. M. Khalil, Fracture and Structural Integrity, 72 (2025) 193-210; DOI: 10.3221/IGF-ESIS.72.14

Nominal moment strength of steel reinforced only The first principles procedure involves calculating the distance from the neutral axis to the end of compressed concrete by producing the corresponding stress level and confirming the equilibrium of internal force. In case of non equilibrium, the neutral axis depth should be updated and the steps are repeated. The resisting moments are obtained from Eqn. 3 according to Egyptian code of practice (ECP-203) [27] .                 n s s y s s a M A A f d A f d d ' ' ' 2 (3) Nominal moment strength of internal GFRP composite beams The internal strain and stress distribution for the composite beam specimen under flexure at the ultimate limit state is shown in Fig. 14.

RC section Equivalent stress Figure 14: Internal strain and stress distribution of composite sec. at ultimate limit state. Resisting moments for composite beams with steel I-sections can be found according to AISC 360 [28] and Eurocode 4 [29] from the theoretical Eqn. 4 .                         n s s y s y s s a a M A A f d A f d A f d d ' ' ' 2 2 (4) Therefore, the resisting moments for GFRP I-sections can be calculated by modifying the previse Eqn. 4 to proposed theoretical Eqn. 5.                         n s s y s fe f s s a a M A A f d A f d A f d d ' ' ' 2 2 (5) Strain Nonlinear stress

  fe f f f E

(6)

 d c

f





 f

 f

allowable

0.003

(7)

c

where:

A f The area of the GFRP I-section d f The distance from the extreme compression concrete fiber to the center of the GFRP E f Tensile modulus of elasticity of GFRP f fe Effective stress in the GFRP I-section; stress level attained at section failure k f Sliding coefficient between an external GFRP I-section and concrete equal to 0.75 ε f The strain in the GFRP

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